The genes of the coactivator TIF2 and the corepressor SMRT are primary 1alpha,25(OH)2D3 targets

Effects of 1,25-Dihydroxy vitamin D3 on TNF-α induced inflammation in human chondrocytes and SW1353 cells: a possible role for toll-like receptors

The purpose of this study is to evaluate anti-inflammatory and chondro-protective effects of 1,25(OH)₂D₃ in human chondrocytes and SW1353 cells via investigating expressions of MMPs, TIMPs, VDR, and intracellular signalling pathway mediators such as TLR-2 and -4. The HC and SW1353 cells were treated with 1,25(OH)₂D₃ at 10, 100, and 1000 nM concentrations in the absence/presence of TNF-α (20 ng/mL) for 48 h. The mRNA expressions of MMP-1, -2, -3, -9, and -13, TIMP-1 and -2, VDR, TLR-2 and -4 in HC and SW1353 cells were detected by qPCR after treatments. The cytotoxicity and cell proliferation analyses were assessed by LDH and WST-1 assay, respectively. Protein levels of MMPs, TIMPs, and VDR were analysed by immunocytochemistry and ELISA methods. TNF-α markedly increased cytotoxicity for 24, 48, 72 h (p < 0.05) and vitamin D treatment was shown to diminish the cytotoxic effect of TNF-α. Cell proliferations increased by Vitamin D in a dose-dependent manner. mRNA expressions of MMP-1, -2, -3, -9, and -13, TLR-2 and -4 genes decreased with 1,25(OH)₂D₃ treatment (p < 0.05). VDR, TIMP-1 and -2 levels elevated after TNF-α exposure compared with the control group in HC cells (p < 0.05). Protein expression levels were determined using Western blotting, ELISA and immunocytochemistry. 1,25(OH)₂D₃ via binding to VDR, reversed the effects of TNF-α by inhibiting TLR-2 and 4. Decreased levels of VDR, TIMP-1 and -2 after TNF-α treatment were elevated by 1,25(OH)₂D₃ proportional with increasing 1,25(OH)₂D₃ doses. 1,25(OH)₂D₃ and TNF-α co-treatment decreased MMP-1, -2, -3, -9, and -13 levels were after TNF-α exposure.

Vitamin D receptor and RXR in the post-genomic era

Following the elucidation of the human genome and components of the epigenome, it is timely to revisit what is known of vitamin D receptor (VDR) function. Early transcriptomic studies using microarray approaches focused on the protein coding mRNA that were regulated by the VDR, usually following treatment with ligand. These studies quickly established the approximate size and surprising diversity of the VDR transcriptome, revealing it to be highly heterogenous and cell type and time dependent. Investigators also considered VDR regulation of non-protein coding RNA and again, cell and time dependency was observed. Attempts to integrate mRNA and miRNA regulation patterns are beginning to reveal patterns of co-regulation and interaction that allow for greater control of mRNA expression, and the capacity to govern more complex cellular events. Alternative splicing in the trasncriptome has emerged as a critical process in transcriptional control and there is evidence of the VDR interacting with components of the splicesome. ChIP-Seq approaches have proved to be pivotal to reveal the diversity of the VDR binding choices across cell types and following treatment, and have revealed that the majority of these are non-canonical in nature. The underlying causes driving the diversity of VDR binding choices remain enigmatic. Finally, genetic variation has emerged as important to impact the transcription factor affinity towards genomic binding sites, and recently the impact of this on VDR function has begun to be considered.

Nuclear receptors and the Warburg effect in cancer

In 1927 Otto Warburg established that tumours derive energy primarily from the conversion of glucose to lactic acid and only partially through cellular respiration involving oxygen. In the 1950s he proposed that all causes of cancer reflected different mechanisms of disabling cellular respiration in favour of fermentation (now termed aerobic glycolysis). The role of aberrant glucose metabolism in cancer is now firmly established. The shift away from oxidative phosphorylation towards the metabolically expensive aerobic glycolysis is somewhat counter-intuitive given its wasteful nature. Multiple control processes are in place to maintain cellular efficiency and it is likely that these mechanisms are disrupted to facilitate the shift to the reliance on aerobic glycolysis. One such process of cell control is mediated by the nuclear receptor superfamily. This large family of transcription factors plays a significant role in sensing environmental cues and controlling decisions on proliferation, differentiation and cell death for example, to regulate glucose uptake and metabolism and to modulate the actions of oncogenes and tumour suppressors. In this review we highlight mechanisms by which nuclear receptors actions are altered during tumorigenic transformation and can serve to enhance the shift to aerobic glycolysis. At the simplest level, a basic alteration in NR behaviour can serve to enhance glycolytic flux thus providing a basis for enhanced survival within the tumour micro-environment. Ameliorating the enhanced NR activity in this context may help to sensitize cancer cells to Warburg targeted therapies and may provide future drug targets.

Vitamin D and the RNA transcriptome: more than mRNA regulation

The GRCh37.p13 primary assembly of the human genome contains 20805 protein coding mRNA, and 37147 non-protein coding genes and pseudogenes that as a result of RNA processing and editing generate 196501 gene transcripts. Given the size and diversity of the human transcriptome, it is timely to revisit what is known of VDR function in the regulation and targeting of transcription. Early transcriptomic studies using microarray approaches focused on the protein coding mRNA that were regulated by the VDR, usually following treatment with ligand. These studies quickly established the approximate size, and surprising diversity of the VDR transcriptome, revealing it to be highly heterogenous and cell type and time dependent. With the discovery of microRNA, investigators also considered VDR regulation of these non-protein coding RNA. Again, cell and time dependency has emerged. Attempts to integrate mRNA and miRNA regulation patterns are beginning to reveal patterns of co-regulation and interaction that allow for greater control of mRNA expression, and the capacity to govern more complex cellular events. As the awareness of the diversity of non-coding RNA increases, it is increasingly likely it will be revealed that VDR actions are mediated through these molecules also. Key knowledge gaps remain over the VDR transcriptome. The causes for the cell and type dependent transcriptional heterogenetiy remain enigmatic. ChIP-Seq approaches have confirmed that VDR binding choices differ very significantly by cell type, but as yet the underlying causes distilling VDR binding choices are unclear. Similarly, it is clear that many of the VDR binding sites are non-canonical in nature but again the mechanisms underlying these interactions are unclear. Finally, although alternative splicing is clearly a very significant process in cellular transcriptional control, the lack of RNA-Seq data centered on VDR function are currently limiting the global assessment of the VDR transcriptome. VDR focused research that complements publically available data (e.g., ENCODE Birney et al., 2007; Birney, 2012), TCGA (Strausberg et al., 2002), GTEx (Consortium, 2013) will enable these questions to be addressed through large-scale data integration efforts.

Vitamin D - effects on skeletal and extraskeletal health and the need for supplementation

Vitamin D, the sunshine vitamin, has received a lot of attention recently as a result of a meteoric rise in the number of publications showing that vitamin D plays a crucial role in a plethora of physiological functions and associating vitamin D deficiency with many acute and chronic illnesses including disorders of calcium metabolism, autoimmune diseases, some cancers, type 2 diabetes mellitus, cardiovascular disease and infectious diseases. Vitamin D deficiency is now recognized as a global pandemic. The major cause for vitamin D deficiency is the lack of appreciation that sun exposure has been and continues to be the major source of vitamin D for children and adults of all ages. Vitamin D plays a crucial role in the development and maintenance of a healthy skeleton throughout life. There remains some controversy regarding what blood level of 25-hydroxyvitamin D should be attained for both bone health and reducing risk for vitamin D deficiency associated acute and chronic diseases and how much vitamin D should be supplemented.

Hypovitaminosis D as predisposing factor for atrophic type A gastritis: a case-control study and review of the literature on the interaction of Vitamin D with the immune system

1,25-Dihydroxyvitamin D displays immunoregulatory and anti-inflammatory properties, and the cells involved in innate and adaptive immune response express the vitamin D receptor and can both produce and respond to this hormone. This article aims at describing the complex immune regulatory role of vitamin D and depicting whether a correlation exists between atrophic type A gastritis and hypovitaminosis. We studied 62 autoimmune gastritis (AIG) patients and compared them to 54 lymphocytic gastritis patients, 21 Helicobacter pylori gastritis patients and 212 healthy subjects. We also statistically analyzed vitamin D concentration in 36,384 outpatients referred to our clinical laboratories. 25-Hydroxyvitamin D levels, the measurable metabolite used to determine vitamin D status in plasma, were measured by a chemiluminescent method. Average level of 25-OHD in AIG subjects was 9.8 ± 5.6 ng/mL (95% confidence interval (CI) 8.4-11.2), 11.1 ± 8.4 (CI 7.5-14.7) in H. pylori gastritis patients, 22.2 ± 13.5 (CI 18.6-25.8) in nonspecific lymphocytic gastritis patients, 21.3 ± 12.2 (CI 19.7-22.9) in healthy subjects, and 21.8 ± 13.1 (CI 21.7-21.9) in the 36,384 outpatients. Vitamin D levels in AIG patients were significantly lower than in patients with nonspecific gastritis or in the general population, supporting the hypothesis that hypovitaminosis D might be a risk factor for the development of autoimmune diseases. The low vitamin D concentration in H. pylori gastritis patients might act as predisposing factor for a more severe Th1-type aggression to the stomach epithelium.

HDAC inhibitors sodium butyrate and sodium valproate do not affect human ncor1 and ncor2 gene expression in HL-60 cells

AIM. This study was designed to examine whether the class I and class IIa histone deacetylase (HDAC) inhibitors, sodium butyrate and sodium valproate alter the expression of human NCOR1 and/or NCOR2 genes coding for N-CoR (nuclear receptor corepressor) and SMRT (silencing mediator for retinoid and thyroid hormone receptors), respectively.

METHODS

Human leukemia HL-60 cells were treated for 24 h with 0.5 and 1 mM sodium butyrate, 1 to 3 mM sodium valproate, 1 mcM all-trans retinoic acid (ATRA) or cotreated with 1 mcM ATRA and 0.5 mM sodium butyrate. The acetylation of histones H3 and H4 was analysed by western blotting. The levels of NCOR1 and NCOR2 mRNA were determined by quantitative real-time PCR. Expression of NCF2 gene coding for the NADPH oxidase subunit p67phox was evaluated as a marker of myeloid differentiation. Results. Both butyrate and valproate increased the acetylation of histone H3 at Lys9 and/or Lys14 as well as histone H4 at Lys12. Both HDAC inhibitors caused a significant increase in NCF2 mRNA levels without affecting NCOR1 or NCOR2 mRNA levels. Similarly, ATRA alone or in combination with butyrate induced NCF2 gene expression without any significant influence on the expression of NCOR1 or NCOR2 genes.

CONCLUSION

We conclude that inhibitors of class I and class IIa HDACs do not alter the expression of human NCOR1 or NCOR2 genes and that the onset of myeloid differentiation is not accompanied by induction or repression of these genes in HL-60 cells.

Cellular content of UDP-N-acetylhexosamines controls hyaluronan synthase 2 expression and correlates with O-linked N-acetylglucosamine modification of transcription factors YY1 and SP1

Hyaluronan, a high molecular mass polysaccharide on the vertebrate cell surface and extracellular matrix, is produced at the plasma membrane by hyaluronan synthases using UDP-GlcNAc and UDP-GlcUA as substrates. The availability of these UDP-sugar substrates can limit the synthesis rate of hyaluronan. In this study, we show that the cellular level of UDP-HexNAc also controls hyaluronan synthesis by modulating the expression of HAS2 (hyaluronan synthase 2). Increasing UDP-HexNAc in HaCaT keratinocytes by adding glucosamine down-regulated HAS2 gene expression, whereas a decrease in UDP-HexNAc, realized by mannose treatment or siRNA for GFAT1 (glutamine:fructose-6-phosphate amidotransferase 1), enhanced expression of the gene. Tracing the UDP-HexNAc-initiated signal to the HAS2 promoter revealed no change in the binding of STAT3, NF-κB, and cAMP response element-binding protein, shown previously to mediate growth factor and cytokine signals on HAS2 expression. Instead, altered binding of SP1 and YY1 to the promoter correlated with cellular UDP-HexNAc content and inhibition of HAS2 expression. siRNA silencing of YY1 and SP1 confirmed their inhibitory effects on HAS2 expression. Reduced and increased levels of O-GlcNAc-modified SP1 and YY1 proteins were associated with stimulation or inhibition of HAS2 expression, respectively. Our data are consistent with the hypothesis that, by regulating the level of protein O-GlcNAc modifications, cellular UDP-HexNAc content controls HAS2 transcription and decreases the effects on hyaluronan synthesis that would result from cellular fluctuations of this substrate.

Primary effect of 1α,25(OH)₂D₃ on IL-10 expression in monocytes is short-term down-regulation

The biologically most active vitamin D compound, 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃), influences the status of inflammation by modulating the expression of several cytokine genes. In this study, we have examined the mechanism of transcriptional regulation of interleukin 10 (IL-10) by 1α,25(OH)₂D₃ in lipopolysaccharide (LPS)-treated human monocytes (THP-1). Quantitative PCR showed that IL-10 mRNA expression was significantly down-regulated (2.8-fold) during the first 8h of 1α,25(OH)₂D₃ treatment, while after 48 h it was up-regulated (3-fold). Gel shift and quantitative chromatin immunoprecipitation (ChIP) assays showed that the vitamin D receptor (VDR) binds in a cyclical fashion to a promoter region 1500-1700 bp upstream of the IL-10 transcription start site (TSS) containing two conserved VDR binding sites. Targeting of VDR binding sites by enhancer specific duplex RNAs revealed that only the more distal element is functional and chromosome conformation capture analysis suggested that this region loops 1α,25(OH)₂D₃-dependently to the TSS. Quantitative ChIP and micrococcal nuclease assays also revealed 1α,25(OH)₂D₃-dependent cyclical epigenetic changes and nucleosome remodeling at this promoter region. In conclusion, in LPS-treated THP-1 cells the primary effect of 1α,25(OH)₂D₃ on IL-10 expression is down-regulation, which is achieved via a cyclical recruitment of VDR to the promoter.

The down-regulation of the human MYC gene by the nuclear hormone 1alpha,25-dihydroxyvitamin D3 is associated with cycling of corepressors and histone deacetylases

MYC is a pleiotropic transcription factor that coordinates the expression of diverse programs that are together necessary for the growth and expansion of somatic cells. The nuclear hormone 1alpha,25-dihydroxyvitamin D(3) down-regulates MYC expression, but the exact mechanism is still elusive. We found in RWPE-1 normal human prostate cells that 1alpha,25-dihydroxyvitamin D(3) down-regulates MYC mRNA with a periodicity of 30-90 min. In silico screening of the MYC gene locus identified six putative binding sites [vitamin D response elements (VDREs)] for the vitamin D receptor (VDR). Two of these VDREs efficiently bound VDR-retinoid X receptor heterodimers in vitro, and their genomic regions associated with VDR in RWPE-1 cells. Gene-specific small inhibitory RNA silencing indicated that basal MYC mRNA expression, as well as its down-regulation, depended on the exchange factor TBL1X (transducer beta-like 1, X-linked), the corepressor silencing mediator for retinoid and thyroid hormone receptor, and histone deacetylases (HDACs) 2, 6, and 11. Assaying the association of these five proteins with the VDRE-containing genomic regions of the MYC gene locus showed characteristic ligand-dependent profiles of TBL1X, silencing mediator for retinoid and thyroid hormone receptor, HDAC6, and HDAC11, in particular on an evolutionarily conserved VDRE. In conclusion, our data suggest that dynamically composed protein complexes that dock via VDR to the two VDREs may explain the repression of the MYC gene.

Cell cycle regulatory effects of retinoic Acid and forskolin are mediated by the cyclin C gene

As a partner of cyclin-dependent kinase (CDK) 3, Cyclin C controls cellular proliferation and, together with CDK8, represses gene transcription. In this study, we showed that the highly expressed Cyclin C gene is a direct target of the nuclear hormone all-trans retinoic acid (RA) in HEK293 human embryonal kidney cells. The RA receptor (RAR) gamma associates with a Cyclin C promoter region containing two RAR binding sites. The Cyclin C gene also directly responds to the cAMP activator Forskolin via the transcription factor CREB1 (cAMP response element-binding protein 1), for which we identified four binding sites within the first 2250 bp of its promoter. RARgamma and CREB1 show functional convergence via the corepressor NCoR1, which controls in particular the Forskolin response of Cyclin C. The histone deacetylases 1, 5, 6, 7 and 11 are involved in the basal expression of Cyclin C, but in HEK293 and MCF-7 human breast carcinoma cells the antiproliferative effects of the histone deacetylase inhibitor SAHA (suberoylanilide hydroxamic acid) are not mediated by Cyclin C. However, cell cycle progressing effects of all-trans RA and Forskolin are dependent on Cyclin C expression levels. This suggests that the primary regulation of Cyclin C by all-trans RA and Forskolin mediates some of the cell cycle control actions of these compounds.

Regulation of the hyaluronan synthase 2 gene by convergence in cyclic AMP response element-binding protein and retinoid acid receptor signaling

The human hyaluronan synthase 2 (HAS2) gene encodes for an enzyme making hyaluronan, altered concentrations of which are associated with many pathological situations including wounding, several inflammatory conditions, and malignant tumors. In this study we showed that HAS2 is a primary target of the cAMP activator forskolin and the nuclear hormone all-trans-retinoic acid (RA). The first 2250 bp of the promoter contain three response elements (REs) for the transcription factor CREB1 as well as two REs for the nuclear receptor RAR. Chromatin immunoprecipitation and re-chromatin immunoprecipitation assays using selected fragments of the promoter containing the putative REs showed that forskolin and all-trans-RA modulate the formation of complexes between CREB1 and RAR with various co-regulators at the predicted sites. Interestingly, CREB1 complexes are regulated by all-trans-RA as are RAR complexes by forskolin. Reporter gene assays using nested promoter fragments supported these findings. Forskolin and all-trans-RA co-stimulation reduced the binding of CREB1, RAR, and the co-repressor nuclear receptor co-repressor 1 (NCoR1), but enhanced the association of co-activators MED1 and CREB-binding protein (CBP). RNA interference experiments suggested that MED1 and NCoR1 are central for the all-trans-RA induction of the HAS2 gene and CBP dominates its forskolin response. In general, our findings suggest a convergence of CREB1 and RAR signaling, and demonstrate the individual character of each RE in terms of co-regulator use.

Estrogen receptor alpha/beta, AIB1, and TIF2 in colorectal carcinogenesis: do coregulators have prognostic significance?

PURPOSE

Estrogen receptor beta (ER beta) is abundantly expressed in colorectal tissue, but its role in colorectal carcinogenesis remains elusive. Estrogen receptor coregulators, amplified in breast cancer 1 (AIB1) and transcription intermediary factor 2 (TIF2), have been well-characterized, but their expression in colorectal carcinomas has not been investigated.

MATERIALS AND METHODS

Estrogen receptor alpha (ER alpha), ER beta, AIB1, and TIF2 protein expression were evaluated by immunohistochemistry in colorectal normal mucosa, adenomas, and adenocarcinomas from 110 patients with colorectal cancer.

RESULTS

ER alpha expression was rare in colorectal tissue and its expression does not appear to be associated with colorectal carcinogenesis. ER beta, AIB1, and TIF2 were detected in the nucleus of epithelial, endothelial, inflammatory, smooth muscle cells, and myofibroblasts. The expression of the three proteins was significantly increased in epithelial cells of carcinomas compared to normal mucosa. In carcinomas, a significant correlation between the levels of expression of AIB1 and TIF2 was noted. Although AIB1 overexpression was associated with local tumor invasion, it was also found to correlate independently with prolonged overall survival.

CONCLUSIONS

ER beta, AIB1, and TIF2 appear to be involved in colorectal tumorigenesis and might have prognostic significance.

Elevated NCOR1 disrupts a network of dietary-sensing nuclear receptors in bladder cancer cells

Increasingly invasive bladder cancer cells lines displayed insensitivity toward a panel of dietary-derived ligands for members of the nuclear receptor superfamily. Insensitivity was defined through altered gene regulatory actions and cell proliferation and reflected both reduced receptor expression and elevated nuclear receptor corepressor 1 (NCOR1) expression. Stable overexpression of NCOR1 in sensitive cells (RT4) resulted in a panel of clones that recapitulated the resistant phenotype in terms of gene regulatory actions and proliferative responses toward ligand. Similarly, silencing RNA approaches to NCOR1 in resistant cells (EJ28) enhanced ligand gene regulatory and proliferation responses, including those mediated by peroxisome proliferator-activated receptor (PPAR) gamma and vitamin D receptor (VDR) receptors. Elevated NCOR1 levels generate an epigenetic lesion to target in resistant cells using the histone deacetylase inhibitor vorinostat, in combination with nuclear receptor ligands. Such treatments revealed strong-additive interactions toward the PPARgamma, VDR and Farnesoid X-activated receptors. Genome-wide microarray and microfluidic quantitative real-time, reverse transcription-polymerase chain reaction approaches, following the targeting of NCOR1 activity and expression, revealed the selective capacity of this corepressor to govern common transcriptional events of underlying networks. Combined these findings suggest that NCOR1 is a selective regulator of nuclear receptors, notably PPARgamma and VDR, and contributes to their loss of sensitivity. Combinations of epigenetic therapies that target NCOR1 may prove effective, even when receptor expression is reduced.

The effect of differentiation on 1,25 dihydroxyvitamin D-mediated gene expression in the enterocyte-like cell line, Caco-2

We examined 1,25 dihydroxyvitamin D (1,25(OH)(2)D(3))-induced expression of 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24) and apical calcium channel (TRPV6) mRNA levels in 2-, 9-, and 15-day cultures Caco-2 cells that model proliferating, post-proliferative, and differentiated enterocytes. 1,25(OH)(2)D(3)-induced (10 nM, 8 h) CYP24 and TRPV6 mRNA levels were significantly greater in differentiated and post-proliferative than proliferating Caco-2 cells (>16X and >3X, respectively). Neither CYP24 mRNA half-life nor induction of a -298 bp rat CYP24 promoter-luciferase reporter construct (10 nM 1,25(OH)(2)D(3), 24 h) were different between proliferating and post-proliferating Caco-2 cells. We next tested whether the blunted response of natural genes to 1,25(OH)(2)D(3) in proliferating Caco-2 cells is due to altered chromatin remodeling. VDR and coactivator protein levels do not increase with differentiation but the level of the co-repressor Alien falls by 50% with differentiation. Over-expression of Alien reduced 1,25(OH)(2)D(3)-induced activity of a minimal VDRE containing promoter-luciferase construct by more than 60% in differentiated Caco-2 cells while siRNA knockdown of Alien in proliferating Caco-2 cells increased 1,25(OH)(2)D(3)-induced CYP24 mRNA level by 40%. These observations suggest that Alien is a regulator of VDR-mediated gene transcription in Caco-2 cells. In addition, we found that 1,25(OH)(2)D(3)-induced association of VDR with chromatin and with the CYP24 promoter was lower in proliferating cells. This suggests that decreased recruitment of VDR to vitamin D response elements also contributes to the blunted transcriptional responsiveness to 1,25(OH)(2)D(3) in proliferating Caco-2 cells.

1alpha,25-Dihydroxyvitamin D3 down-regulates expression of prostate specific membrane antigen in prostate cancer cells

BACKGROUND

Prostate specific membrane antigen (PSMA) expression correlates with prostate cancer grade and is increased in hormone-refractory prostate cancer. The increased expression of PSMA following androgen deprivation therapy may be a consequence of the down-regulation of PSMA expression by androgen. Moreover, 1alpha,25-dihydroxyvitamin D3 (1,25-VD) has been shown to suppress prostate cancer progression as well as cell motility and invasion. Since PSMA is positively correlated with both of these characteristics, we hypothesized that 1,25-VD would regulate PSMA expression.

METHODS

LNCaP prostate cancer cells were treated with 1,25-VD, followed by analysis of cell surface PSMA expression. The PSMA enhancer, located within the third intron of the PSMA gene, was cloned into a reporter vector and regulation by 1,25-VD was investigated. The role of the androgen receptor (AR) in 1,25-VD mediated suppression of PSMA expression was examined using Casodex and AR specific siRNA.

RESULTS

Surface expression of PSMA was significantly decreased in a dose-dependent manner by 10 nM 1,25-VD or greater. Regulation by 1,25-VD occurred at the level of the PSMA enhancer. Over-expression of the vitamin D receptor (VDR) also decreased expression of PSMA. Additionally, suppression of AR translation using siRNA technology blocked the suppressive effect of 1,25-VD on PSMA expression, however inhibition of PSMA expression by 1,25-VD occurred in the absence of androgens.

CONCLUSIONS

Suppression of PSMA by 1,25-VD occurs at the level of the PSMA enhancer and is elevated by over-expression of the VDR. This regulation involves the AR, but is not dependent on the presence of androgens.

Integration of the activation of the human hyaluronan synthase 2 gene promoter by common cofactors of the transcription factors retinoic acid receptor and nuclear factor kappaB

Hyaluronan (HA) is a polysaccharide of the vertebrate extracellular matrix, produced by three related HA synthases (HASs) that influence numerous physiological processes. We screened the first 2250 bp of the HAS2 promoter for transcription factor response elements (REs) in silico and found 1 cluster of 2 retinoic acid (RA) REs, 3 discrete NF-kappaB factors, and 12 Sp1 REs. In parallel, we scanned nine overlapping promoter regions in HaCaT human immortalized keratinocytes using chromatin immunoprecipitation assays to identify binding of mediator, coactivator, and corepressor proteins and Sp1 transcription factor in response to all-trans-RA and tumor necrosis factor-alpha (TNF-alpha). We found that all-trans-RA modulated the binding of the RA receptor and several coregulators to the region containing the RARE cluster at position -1230. The importance of this region is supported in reporter gene assays by the all-trans-RA induction of the respective promoter region. Similarly, we showed by chromatin immunoprecipitation assays as well as by gel-shift assays with nuclear extracts that TNF-alpha induced NF-kappaB binding to regions at positions -380, -1420, and -1890, demonstrated its association with RNA polymerase II and cofactor proteins, and confirmed the functionality of the respective promoter regions in vivo. These findings partially explain the induction of HAS2 mRNA by all-trans-RA and TNF-alpha and provide an example how the action of different transcription factor families can use the same cofactors.

Steroid receptor coregulator diversity: What can it mean for the stressed brain?

Glucocorticoid hormones modulate brain function and as such are crucial for responding and adjusting to physical and psychological stressors. Their effects are mediated via mineralo- and glucocorticoid receptors, which in large measure act as transcription factors to modulate transcription of target genes, in a receptor-, cell-, and state-specific manner. The nature and magnitude of these transcriptional effects depend on the presence and activity of downstream proteins, such as steroid receptor coactivators and corepressors (together: coregulators), many of which are expressed in the brain. We address the role of coregulators for mineralo- and glucocorticoid receptor-mediated modulation of gene transcription. We first address evidence from cell lines for the importance of coregulator stoichiometry for steroid signaling. The in vivo importance of coregulators-when possible specifically for glucocorticoid signaling in the brain-is discussed based on knockout mice, transient knockdown of steroid receptor coactivators, and distribution and regulation of coactivator expression in the brain. We conclude that for a better understanding of modulation of brain function by glucocorticoids, it is necessary to take into account the role of coregulators, and to assess their importance relative to changes in hormone levels and receptor expression.

Transcriptional silencing of Polo-like kinase 2 (SNK/PLK2) is a frequent event in B-cell malignancies

The Polo-like kinases (Plks) are a highly conserved family of protein kinases that function in regulation of cell cycle and DNA damage-induced checkpoints. Evidence of a tumor suppressor function for the Plks in human neoplasia is lacking. Here, we report that Snk/Plk2 is transcriptionally down-regulated in B-cell neoplasms. Silencing occurs with very high frequency in Burkitt lymphoma (BL) but is also detected in B-cell neoplasms of other types and is associated with aberrant cytosine methylation in the CpG island located at the 5' end of the SNK/PLK2 gene. Silencing is specific to malignant B cells because SNK/PLK2 was unmethylated (and expressed) in primary B lymphocytes, in EBV-immortalized B lymphoblastoid cell lines (LCLs), and in adenocarcinomas (of the breast) and squamous-cell carcinomas (of the head and neck). Expression of Snk/Plk2 in BL cell lines was restored by demethylating agents. The related PLK1 and PLK3 (FNK/PRK) genes were overexpressed in BL cell lines lacking Snk/Plk2 expression, consistent with functional degeneracy among the Plk family. Ectopic expression of Snk/Plk2 in BL cells resulted in apoptosis, a potential mechanistic basis underlying the strong selective pressure for abrogation of Snk/Plk2 function in B-cell neoplasia.

Vitamin D

The vitamin D endocrine system plays an essential role in calcium homeostasis and bone metabolism, but research during the past two decades has revealed a diverse range of biological actions that include induction of cell differentiation, inhibition of cell growth, immunomodulation, and control of other hormonal systems. Vitamin D itself is a prohormone that is metabolically converted to the active metabolite, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. This vitamin D hormone activates its cellular receptor (vitamin D receptor or VDR), which alters the transcription rates of target genes responsible for the biological responses. This review focuses on several recent developments that extend our understanding of the complexities of vitamin D metabolism and actions: the final step in the activation of vitamin D, conversion of 25-hydroxyvitamin D to 1,25(OH)(2)D in renal proximal tubules, is now known to involve facilitated uptake and intracellular delivery of the precursor to 1alpha-hydroxylase. Emerging evidence using mice lacking the VDR and/or 1alpha-hydroxylase indicates both 1,25(OH)(2)D(3)-dependent and -independent actions of the VDR as well as VDR-dependent and -independent actions of 1,25(OH)(2)D(3). Thus the vitamin D system may involve more than a single receptor and ligand. The presence of 1alpha-hydroxylase in many target cells indicates autocrine/paracrine functions for 1,25(OH)(2)D(3) in the control of cell proliferation and differentiation. This local production of 1,25(OH)(2)D(3) is dependent on circulating precursor levels, providing a potential explanation for the association of vitamin D deficiency with various cancers and autoimmune diseases.

The Human Peroxisome Proliferator-activated Receptor δ Gene is a Primary Target of 1α,25-Dihydroxyvitamin D3 and its Nuclear Receptor

Peroxisome proliferator-activated receptor (PPAR) delta is the most widely expressed member of the PPAR family of nuclear receptor fatty acid sensors. Real-time PCR analysis of breast and prostate cancer cell lines demonstrated that PPARdelta expression was increased 1.5 to 3.2-fold after three hours stimulation with the natural vitamin D receptor (VDR) agonist, 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3). In silico analysis of the 20 kb of the human PPARdelta promoter revealed a DR3-type 1alpha,25(OH)2D3 response element approximately 350 bp upstream of the transcription start site, which was able to bind VDR-retinoid X receptor (RXR) heterodimers and mediate a 1alpha,25(OH)2D3-dependent upregulation of reporter gene activity. Chromatin immuno-precipitation assays demonstrated that a number of proteins representative for 1alpha,25(OH)2D3-mediated gene activation, such as VDR, RXR and RNA polymerase II, displayed a 1alpha,25(OH)2D3-dependent association with a region of the proximal PPARdelta promoter that contained the putative DR3-type VDRE. This was also true for other proteins that are involved in or are the subject of chromatin modification, such as the histone acetyltransferase CBP and histone 4, which displayed ligand-dependent association and acetylation, respectively. Finally, real-time PCR analysis demonstrated that 1alpha,25(OH)2D3 and the synthetic PPARdelta ligand L783483 show a cell and time-dependent interference in each other's effects on VDR mRNA expression, so that their combined application shows complex effects on the induction of VDR target genes, such as CYP24. Taken together, we conclude that PPARdelta is a primary 1alpha,25(OH)2D3-responding gene and that VDR and PPARdelta signaling pathways are interconnected at the level of cross-regulation of their respective transcription factor mRNA levels.